The present invention relates to a ferrite chip bead and a method for making the same, and more particularly to a ferrite chip bead capable of being mounted on the surface of a circuit board and its method of manufacture. Ferrite chip beads are well known as elements for removing undesirable electron waves by impedance, which is determined by the amount of ferrite substrate. When current flows through the ferrite substrate, a portion of the frequency band exhibiting high reduced loss is absorbed in the ferrite substrate and discharged as heat (in accordance with the characteristics of ferrite substrate).
Chip beads having the above characteristics are useful as elements for mounting on the surface of a circuit board.
FIG. 4a illustrates a conventional chip bead structure. As shown in FIG. 4a, the chip bead has a double-layered sheet structure comprising a pair of ferrite sheets 1 which constitute a ferrite substrate. Ferrite sheets 1 have facing inner surfaces printed with conductive paste (not shown). The sheet is cut to have a desired size and then subjected to baking. Thereafter, a plurality of outer electrodes [4'] are attached to opposite sides of the sheet structure to form the chip bead. Alternatively, a plurality of transversely extending holes are perforated in the ferrite sheet structure (denoted by the reference numeral 1 in FIG. 4a) prior to printing the conductive paste. Conductive paste 2 is filled into each hole with subsequent processes being the same as mentioned above.
Manufacture of such a chip bead structure is troublesome since ferrite paste is printed on each sheet or filled in holes perforated in the ferrite sheet structure. Moreover, inner conductors formed by printing conductive paste have small area and weak bonding due to their structure. As a result, there exists problems with poor contact between inner conductors and outer electrodes and a tendency for outer electrodes to short-circuit from the ferrite substrate upon placement of the chip bead on a circuit board. Since the inner conductors have a microstructure, they may be varied in electric characteristic (upon baking), together with the ferrite substrate.
The above stated disadvantages prevent known chip bead structures from use in electrical circuits requiring a high level of reliability.